This invention relates to dynamoelectric machines and, in particular, to dynamoelectric machines of the type including a rotating field comprising electrically conductive windings disposed in a plurality of axially extending slots.
The rotating field of a dynamoelectric machine includes a rotor body having a plurality of axially extending slots into which the electrical windings are inserted. The rotor body is generally a steel material whereas the rotor windings comprise a plurality of copper wires. In a direct-cooled dynamoelectric machine each slot may further include an axially extending sub-slot for ventilation and cooling. The direct-cooled machine is one which is cooled directly by the atmosphere in which it is disposed; e.g., air or hydrogen. The sub-slots are part of a ventilation scheme, known in the art, for transferring gas coolant axially along the rotor. Each slot also includes provision for the radial flow of gas coolant primarily through ventilation slots in the windings.
In the aforementioned machine it is necessary to electrically insulate the rotor windings from the rotor body such insulation taking the form of non-conductive "slot armor". One such insulation is shown in U.S. Pat. No. 4,321,498 to Vogt and assigned to the assignee of the present invention. In that patent herein incorporated by reference, it is suggested that a preferred embodiment of the invention would include a pair of electrical insulating members (slot armor), each member comprising a radially extending portion terminating in a base leg, the electrically insulating members disposed in each slot so that the radially extending portions are adjacent opposite slot walls and the base legs extend towards on another. In addition, there is an axially extending base (sub-slot cover) having opposite sides formed with axially extending grooves for accepting therein each opposite base leg whereby an interlocking joint is formed between the sub-slot cover and the slot armor. It is further suggested that both the sub-slot cover and the insulating slot armor disposed adjacent the slot walls would be formed from glass laminate material.
The applicants have found it desirable to use an aramid paper such as Nomex (trademark, DuPont Company) as an insulating material for the slot armor. However, in following the teaching of the previous U.S. Pat. No. 4,321,498 they have found that there is a lack of rigidity which occurs in the 90.degree. bend at the interlocking section of the insulating member and the base member. Under centrifugal load, the slot armor will migrate up the slot wall pulling away from the interlocking section of the sub-slot.
Aramid paper is presently used in conventionally-cooled machines only. Conventionally-cooled machines are described as other than direct-cooled machines. Conventionally-cooled machines are machines wherein cooling of the windings occurs by transfer of heat from the windings through the body of the rotor and then into the cooling medium. In the direct-cooled machine, the cooling medium is passed directly through the windings. Aramid paper will exhibit dimensional instability and can increase axially in length as much as one percent under changing conditions of relative humidity. Therefore, even U-shaped aramid paper with punched ventilation slots has been avoided in direct-cooled fields because changes in humidity can cause the register of the ventilation slots for the sub-slot cover-slot armor and copper to become misaligned, thus reducing the area of cooling paths.
It is therefore an object of the invention to provide an improved slot insulation for a dynamoelectric machine which includes aramid paper as the slot wall insulation.
It is another object of the invention to provide an improved slot insulation for a dynamoelectric machine which is a composite of aramid paper side-wall insulation and a glass laminate and aramid paper base member.
It is a further object of the invention to provide a composite slot insulation for a dynamoelectric machine wherein the base member controls and renders rigid the tendency of the aramid paper to grow.
The novel features believed characteristic of the present invention are set forth in the appended claims. The invention itself, however, together with further objects and advantages thereof, may best be understood with reference to the following description taken in conjunction with the appended drawings.